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PDF LM2619ATLX Data sheet ( Hoja de datos )
| Número de pieza | LM2619ATLX | |
| Descripción | 500mA Sub-Miniature Step-Down DC-DC Converter | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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November 2002
LM2619
500mA Sub-Miniature Step-Down DC-DC Converter
General Description
The LM2619 step down DC-DC converter is optimized for
powering circuits from a single Lithium-Ion cell. It steps down
an input voltage of 2.8V to 5.5V to an output of 1.5V to 3.6V
at up to 500mA. Output voltage is set using resistor feedback
dividers.
The device offers three modes for mobile phones and similar
portable applications. Fixed-frequency PWM mode mini-
mizes RF interference. A SYNC input allows synchronizing
the switching frequency in a range of 500kHz to 1MHz. Low
current hysteretic PFM mode reduces quiescent current to
160µA (typ.). Shutdown mode turns the device off and re-
duces battery consumption to 0.02µA (typ.).
Current limit and thermal shutdown features protect the de-
vice and system during fault conditions.
The LM2619 is available in a 10 bump micro SMD package.
This packaging uses National’s chip-scale micro SMD tech-
nology and offers the smallest possible size. A high switching
frequency (600kHz) allows use of tiny surface-mount com-
ponents.
The device features external compensation to tailor the re-
sponse to a wide range of operating conditions.
Key Specifications
n Operates from a single LiION cell (2.8V to 5.5V)
n Output voltage (1.5V to 3.6V)
n ±1% DC feedback voltage precision
n 500mA maximum load capability
n 600µA typ PWM mode quiescent current
n 0.02µA typ shutdown current
n 600kHz PWM switching frequency
n SYNC input for PWM mode frequency synchronization
from 500kHz to 1MHz
n High efficiency (96% typ at 3.9VIN, 3.6VOUT and 200mA)
in PWM mode from internal synchronous rectification
n 100% Maximum Duty Cycle for Lowest Dropout
Features
n Sub-miniature 10-bump thin micro SMD package
n Uses small ceramic capacitors
n 5mV typ PWM mode output voltage ripple(COUT = 22µF)
n Internal soft start
n Current overload protection
n Thermal Shutdown
n External compensation
Applications
n Mobile Phones
n Hand-Held Radios
n RF PC Cards
n Wireless LAN Cards
© 2002 National Semiconductor Corporation DS200574
www.national.com
1 page  
Typical Performance Characteristics LM2619ATL, Circuit of Figure 3, VIN = 3.6V, TA = 25˚C, un-
less otherwise noted.
Quiescent Supply Current vs Supply Voltage
Shutdown Quiescent Current vs Temperature
(Circuit in Figure 3)
20057408
Output Voltage vs Supply Voltage
(VOUT = 1.5V, PWM MODE)
20057422
Output Voltage vs Supply Voltage
(VOUT = 1.5V, PFM MODE)
20057409
Output Voltage vs Output Current
(VOUT = 1.5V, PWM MODE)
20057410
Output Voltage vs Output Current
(VOUT = 1.5V, PFM MODE)
20057411
5
20057413
www.national.com
5 Page 
Device Information (Continued)
less than the 2.8V minimum operating voltage. The LM2619
is designed for compact portable applications, such as mo-
bile phones. In such applications, the system controller de-
termines power supply sequencing. Although the LM2619 is
typically well behaved at low input voltages, this is not guar-
anteed.
INTERNAL SYNCHRONOUS RECTIFICATION
While in PWM mode, the LM2619 uses an internal NFET as
a synchronous rectifier to reduce rectifier forward voltage
drop and associated power loss. Synchronous rectification
provides a significant improvement in efficiency whenever
the output voltage is relatively low compared to the voltage
drop across an ordinary rectifier diode.
The internal NFET synchronous rectifier is turned on during
the inductor current down slope during the second part of
each cycle. The synchronous rectifier is turned off prior to the
next cycle, or when the inductor current ramps to zero at light
loads. The NFET is designed to conduct through its intrinsic
body diode during transient intervals before it turns on, elimi-
nating the need for an external diode.
CURRENT LIMITING
A current limit feature allows the LM2619 to protect itself and
external components during overload conditions. In PWM
mode cycle-by-cycle current limit is normally used. If an
excessive load pulls the voltage at the feedback pin down to
approximately 0.7V, then the device switches to a timed
current limit mode. In timed current limit mode the internal
P-FET switch is turned off after the current comparator trips
and the beginning of the next cycle is inhibited for 2.5µs to
force the instantaneous inductor current to ramp down to a
safe value. Timed current limit mode prevents the loss of
current control seen in some products when the voltage at
the feedback pin is pulled low in serious overload conditions.
DROPOUT CONSIDERATIONS
The LM2619 can be used to provide fixed output voltages by
using external feedback resistors. The output voltage can be
set from 1.5V to 3.6V. The internal reference voltage for the
error amplifier is 1.5V. In cases where the output voltage is
set higher than 2.5V, the part will go into dropout or 100%
duty cycle when the input voltage gets close to the set output
voltage. Near dropout the on time of the P-FET may exceed
one PWM clock cycle and cause higher ripple on the output
for load currents greater than 450mA. This increased ripple
will exist for a narrow range of input voltages close to the
100% duty cycle and once the input voltage goes down
further the P-FET will be fully on. See Setting the Output
Voltage in the Application Information section for further
details.
In dropout conditions the output voltage is VIN − IOUT (Rdc +
RDSON (P)) where Rdc is the series resistance of the inductor
and RDSON (P) is the on resistance of the PFET.
Load Transient Response
(Circuit in Figure 3)
FIGURE 8.
Line Transient Response
(Circuit in Figure 3)
20057427
FIGURE 9.
20057428
SOFT-START
The LM2619 has soft start to reduce current inrush during
power-up and startup. This reduces stress on the LM2619
and external components. It also reduces startup transients
on the power source. Soft start is implemented by ramping
up the reference input to the error amplifier of the LM2619 to
gradually increase the output voltage.
THERMAL SHUTDOWN PROTECTION
The LM2619 has a thermal shutdown protection function to
protect itself from short-term misuse and overload condi-
tions. When the junction temperature exceeds 150˚C the
device turns off the output stage and when the temperature
drops below 130˚C it initiates a soft start cycle. Prolonged
operation in thermal shutdown conditions may damage the
device and is considered bad practice.
11 www.national.com
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| Páginas | Total 15 Páginas | |
| PDF Descargar | [ Datasheet LM2619ATLX.PDF ] | |
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